Difference in Structure and Electronic Properties of Oxygen Vacancies in α-Quartz and α-Cristobalite Phases of SiO(2)

[Formula: see text]-cristobalite ([Formula: see text]-C) is a polymorph of silica, mainly found in space exploration and geochemistry research. Due to similar densities, [Formula: see text]-C is often used as a proxy for amorphous SiO [Formula: see text] , particularly in computer simulations of SiO [Formula: see text] surfaces and interfaces. However, little is known about the properties of [Formula: see text]-C and its basic oxygen defects. Using density functional theory (DFT) simulations we provide a comprehensive report on the properties of perfect structure and oxygen vacancies in [Formula: see text]-C. The calculated properties of [Formula: see text]-C are compared with those of the better-characterized [Formula: see text]-quartz ([Formula: see text]-Q). Our results demonstrated that the positively charged O vacancy in [Formula: see text]-C is most stable in the dimer configuration, in contrast to [Formula: see text]-Q, which favors the puckered configuration. A back-projected configuration was also predicted in both polymorphs. We calculated the optical transition energies and isotropic hyperfine constants for O vacancies in both [Formula: see text]-Q and [Formula: see text]-C, and compared our findings with the results of previous studies and experiments. This work, thus, offers one of the first in-depth investigations of the properties of oxygen vacancies in [Formula: see text]-C.